LIGHTROOM: "Discard all 1:1 Previews" Does Not Work

In Lightroom, "Discard all 1:1 Previews" does not work. I have done this and still have 8GB of preview data in "...Previews.lrdata" folder. I am running LR 5.6 on Win7 x64. I would like to know how to get rid of these previews that are using up valuable space on my SSD.